(1) Field of the Invention
This invention pertains to a shielding material suitable for shielding radioactive rays other than neutron rays.
(2) Prior Art
There have heretofore been generally used concrete or shielding lead blocks as the radiation shielding materials. Such materials have been used as the construction materials in constructing, for example, buildings wherein radioisotopes, X rays, nuclear reactors or like matters are used.
3. Points to be Solved by this Invention:
Concrete structures as mentioned above are required to have not only the necessary structural strength but also a wall thickness which should be determined depending on the amount of radioactive radiation of a radioisotope or the like used in the structures in order to shield the radiation, resulting in very heavy structures compared to ordinary buildings. Since concrete structures are liable to absorb water, they tend to absorb radioactively contaminated water when used in installations wherein radioactive rays are handled, whereas the contaminated water thus absorbed is extremely difficult to remove by washing. In consequence, the concrete structures are normally coated with waterproof paint or overcoated with polymer concrete to reduce or prevent their water absorption, this disadvantageously incurring a great expense. Lead is a very effective shielding material but is very heavy and in addition because of its soft quality, requires much care in construction, thus raising the construction cost.
On the other hand, known radiation shielding materials are prepared from heavy metals or raw ores of them. Generally speaking, the higher the product density is, the greater the primary shielding effect becomes. Accordingly, attempts are being made to obtain shielding products either by molding and solidifying various heavy metal oxides and their ores with cement, an organic curable binder or the like or by compression molding heavy metal compounds and then calcining the molded metal compounds at high temperatures. However, the density of end products is still low although the heavy metal compounds and the like used as the starting materials have their respective inherent high densities, because the starting materials are mixed with various binders depending on uses of the resulting products when they are molded. For this reason, the products or shielding materials thus obtained indicate a low radiation shielding effect and have, as structural material, a strength not greater than that of concrete. Therefore, such shielding materials alone are unsuitable for radioactive shielding purposes. Particularly, the shielding materials in which the organic binder is used has an extremely low strength which is 1/50-1/100 of the strength of concrete. Accordingly, the shielding materials of this sort have simply been used as an auxiliary radiation shielding material by attaching or applying to the surface of concrete structures. Further, many of the binders tend to cause a radical chemical reaction under the irradiation of .gamma. or X rays whereby, with the lapse of time, they are degraded in bonding property and a concrete structure having them used therein is consequently reduced in strength.
As set forth above, although extensive research and development have been made to obtain various kinds of radiation shielding materials, they have advantages and disadvantages and are still unsatisfactory in shielding effects, mechanical strength, water resistance and chemical resistance.